1. Field of the Invention
The present invention relates to a display device using an oxide semiconductor and a method for manufacturing the same.
2. Description of the Related Art
As typically seen in liquid crystal display devices, a thin film transistor formed over a flat plate such as a glass substrate is manufactured using amorphous silicon or polycrystalline silicon. A thin film transistor manufactured using amorphous silicon has low field effect mobility, but can be formed over a larger glass substrate. In contrast, a thin film transistor manufactured using crystalline silicon has high field effect mobility, but due to the necessity of a crystallization step such as laser annealing, such a transistor is not always suitable for being formed over a larger glass substrate.
In view of the foregoing, attention has been drawn to a technique in which a thin film transistor is manufactured using an oxide semiconductor and applied to electronic appliances or optical devices. For example, Patent Document 1 and Patent Document 2 disclose a technique in which a thin film transistor is manufactured using zinc oxide or an In—Ga—Zn—O-based oxide semiconductor for forming an oxide semiconductor film and such a transistor is used as a switching element or the like of an image display device.    Patent Document 1: Japanese Published Patent Application No. 2007-123861    Patent Document 2: Japanese Published Patent Application No. 2007-096055